The present invention relates to a fuel injection system for an internal combustion engine.
Various kinds of fuel injection system are known. For example, Japanese patent laid-open specification No. 55-37525 discloses a fuel injection system which operates to inject fuel in synchronism with the opening time of the fuel-air intake valve in dependency on pulse signals provided by sensing the angular position of a crank arm. Japanese patent laid-open specification No. 55-19933 discloses a system for injecting fuel at the opening times of the fuel-air intake valves of alternate cylinders in the opening order of the valves.
FIG. 4 is a time chart showing the fuel injection timing of a conventional multi-point injection system for an engine having four cylinders (FIG. 1A, 1B and 1C) in which cylinders Nos. 1 and 3 communicate with each other by one common intake manifold section 31 on one side of the engine and cylinders Nos. 2 and 4 communicate with each of the cylinders by another common intake manifold section 30 on another side of the engine. Further both common intake manifold sections 30, 31 communicate with each other via manifold branches 32, 33 connected thereto which in turn are connected to an intake passage 13. By the conventional system, fuel is injected simultaneously into all the common intake manifold sections 30, 31 from fuel injection valves I in each branch 30a, 30b, 31a, 31b (FIG. 1C) of the manifold sections 30, 31 adjacent each cylinder by trigger signals at every alternate ignition timing signal, as shown in FIG. 4 and described below.
In this system, the ignition (timing) signals occur in the intake valve opening order of the cylinders Nos. 1-3-2-4 respectively and are halved in order to produce trigger (pulse) signals for the injection times of all of the injection valves. For example, fuel is injected simultaneously from the respective injection valves I for each of the cylinders upon the occurrence of each of the respective fuel injection (pulse) signals a and b, the latter signals being produced from the trigger signals.
This system with simultaneous injection by all the injection valves saves software and hardware expenses of alternate injection for the fuel injection valves associated with the respective cylinders of the Japanese patent laid-open specification No. 55-19933. Yet defects exist with this system since fuel is unequally distributed into the cylinders with this system.